1. Field of the Invention
The present invention relates to a mobile communication system and a communication controlling method.
2. Description of the Related Art
In a mobile communication system, a communication is performed by using limited resources (frequency and power), and an upper limit on a capacity of the communication is set. Accordingly, an increase of the number of users (the number of mobile stations) who perform the communication in the mobile communication system causes a problem of deteriorating a communication quality of the communication which has been already performed, or a problem that it is not allowed to newly start a communication. This situation is generally called a congestion state.
In addition, in the mobile communication system, in general, priority classes, service types and contract types are provided. Therefore communication services have to be provided in consideration of the priority classes, the service types and the contract types.
More specifically, under the congestion state, the communication quality has to be controlled in consideration of the priority classes, the service types and the contract types. Note that, under a non-congestion state, the communication quality does not have to be controlled seriously, because there seems to be enough resources in the mobile communication system.
For example, a mobile station belonging to the first priority class and a mobile station belonging to the second priority class, which is lower priority than the first priority class, are provided in the mobile communication system. In this case, the mobile station belonging to the second priority class should be treated a lower priority the mobile station belonging to the first priority class.
Meanwhile, the third generation mobile communication system, so-called IMT-2000, has been standardized in 3GPP/3GPP2 (Third-Generation Partnership Project/Third-Generation Partnership Project 2) organized by such as regional standards groups. Precisely, 3GPP defines the standard specifications for the W-CDMA scheme, while 3GPP2 defines the standard specifications for the cdma2000 scheme.
Along with the recent rapid spread of the Internet, 3GPP predicts that high-speed and high-capacity traffic will increase, particularly in a downlink, due to such as downloads from databases and Web sites. Based on this prediction, 3GPP has standardized the specifications of “HSDPA (High Speed Downlink Packet Access)” that is a high-speed downlink packet transmission scheme (for example, see 3GPP TS25. 308 v5.7.0).
In addition, from the same point of view, 3GPP2 also standardizes the specifications of “1x-EV DO” that is a high-speed downlink transmission scheme only for data (for example, see 3GPP2 C. S0024 Rev. 1.0.0). Incidentally, DO in cdma2000 1x-EV DO stands for data only.
More detailed explanation for HSDPA is provided below.
HSDPA is a system in which a plurality of mobile stations perform the communication by sharing a single shared channel. In HSDPA, every time transmission interval (TTI, 2 ms in the case of HSDPA), a base station selects one of the plurality of mobile stations, which is to use the shared channel, and transmits packets to the selected mobile station. It is called as scheduling that the base station selects a mobile station which is to use the shared channel every TTI.
“Round Robin Scheduler” is widely known as a scheduling algorithm in a radio base station. The “Round Robin Scheduler” controls the transmission order of packets waiting for transmission, by assigning the downlink shared channel sequentially to mobile stations (for example, mobile stations #1 to #2 to #3 . . . ) which belong to the radio base station.
Moreover, “Proportional Fairness Scheduler” and “Max C/I (Maximum C/I) Scheduler” are known as scheduling algorithms in a radio base station. The “Proportional Fairness Scheduler” and the “Max C/I Scheduler” control the transmission order of packets waiting for transmission based upon the radio condition of each mobile station and the average transmission rate of packets to each mobile station.
For example, the proportional fairness scheduler performs the scheduling by which an evaluation function,
      C    n    =            R      n                      R        _            n      (where Rn denotes an instantaneous radio condition of each mobile station, and Rn denotes an average transmission rate of each mobile station) is calculated for each mobile station, and by which the shared channel is assigned to a mobile station having the greatest value of the evaluation function Cn.
Here, by adding a factor A showing priority classes to the evaluation function, the proportional fairness scheduling in consideration of the priority classes can be provided. More precisely, by using
      C    n    =      A    ·                  R        n                              R          _                n            as the evaluation function Cn instead of
            C      n        =                  R        n                              R          _                n              ,the proportional fairness scheduling in consideration of the priority classes can be provided.
In other words, in the mobile communication system providing the communication using HSDPA, as for downlink, use of the factor A showing priority classes makes it possible to provide communications in consideration of the aforementioned priority classes, the service types and the contract types.